CLONING AND CHARACTERIZATION OF CANDIDATE GENES FOR APOMIXIS IN KENTUCKY BLUEGRASS (P. pratensis L.)

¹ Department of Plant Biology and Agro-environmental Biotechnology, University of Perugia, Borgo XX Giugno 74, 06121, Perugia, Italy

² Department of Environmental Agronomy and Crop Production, University of Padova, Agripolis, Via Romea 16, 35020 Legnaro, Padova, Italy.

Sex is the queen of problems in evolutionary biology and perhaps no other natural phenomenon has aroused so much interest. One of the escapes from sexuality is represented by apomixis that is as intriguing and exciting as the regular sexual reproduction. In apomixis the avoidance of meiosis leads to the formation of an unreduced embryo sac (apomeiosis) which develops an embryo indipendently from fertilization (parthenogenesis). In some species fertilization may, instead, be needed for endosperm formation. Apomixis has been proposed as a novel pathway distinct from sexual reproduction or as an aberrant form of sexual reproduction. Some works have been carried out to investigate the nature of genes involved in the apomictic reproduction. Using differential and subtractive hybridization some genes have been identified, but comparative spatial and temporal expression in sexual and apomictic plants have not been examined. Genes involved in and known to regulate gametophyte, endosperm, and embryo development have been identified in sexually reproducing plants. We carried out a differential display by using a cDNA-AFLP technique that enabled us to isolate ESTs and candidate genes for apomixis in Kentucky bluegrass (Poa pratensis L.). P. pratensis is an attractive forage and turf grass that reproduces, mainly, through pseudogamous facultative aposporous apomixis. Within an F1 population obtained by crossing a sexual with an highly apomictic genotype, 2 apomictic, 2 sexual and 2 recombinant genotypes were used for the cDNA-AFLP analysis. The cDNA-AFLP approach enabled us to select 172 mRNAs either apomictic- or sexual-specific and to detect transcriptional changes potentially related to apospory and parthenogenesis. The BLAST analysis revealed that about 30% of clones showed no similarity with genes of interest whereas the other 70% showed similarity with genes involved with meiotic or embryo development pathways. The existence of a complex pathway controlling apomixis is commonly assumed. Interestingly, 8 mRNAs differentially expressed between apomictic and sexual genotypes showed a high similarity with a group of genes tightly linked in Arabidopsis thaliana. For these mRNAs we performed a RACE (Rapid amplification of cDNA ends) analysis to obtain the full lenght of the genes. Temporal and spatial characterization of these genes will be reported and discussed.